Ignition live wanted!

[ruaricoles]

Hello peeps,

I've just about finished various cooling system upgrades, but am struggling to find a decent ignition live in the engine bay.

I have a row of chunky 70A relays to switch some hefty fans from series to parallel (for half and full speed at different temps), and tried to use the original wiring for the now redundant otter switch but despite having a good 12V across it with no load, it appears to drop to under 4V as soon as it powers one of the relays leaving it incapable of switching a second when required meaning I never get full fan power. With a separate 12V supply straight from the battery the system works fine. I assume therefore that the otter switch wiring is somewhat on the weedy side??

So, is there anywhere else handy I can take some power from when the ignition is on? I assume the AFM etc. have a suitable feed (?) but I don't want to risk messing up the function of anything else in the process.

I could use the otter switch wire to operate a single small relay to then supply a current for the rest but that seems a bit daft.....

Many thanks

Ruari

[spend]

ruaricoles said:

I could use the otter switch wire to operate a single small relay to then supply a current for the rest but that seems a bit daft.....

Thats actually the only bit that sounds sensible to me

Dave

[griffter]

I wouldn't use anything to do with the ecu signals - the voltage will drop momentarily as the fans switch on and that could cause grief at the ecu.
My otter switch drives two fan relays OK - sorry to ask, but you're taking both relay feeds from the positive side of the otter, and both in parallel? If the otter switch wiring 'sees' only 4v with the first relay on, leaving (for the sake of argument) 8v across the 'on' relay, then that suggests the otter wiring has a resistance equal to half that of the relay primary coil. There's got to be something amiss if that really is the case - the primary winding's normally a couple of hundred ohms. Either trace and find the problem, replace the otter wiring (in which case you might as well just run an ignition switched wire from the fuse box), or do the 'little relay' thing.

Of course the coil positive is ignition switched, but I wouldn't use that either becuase of back EMF voltage spikes and/or the fans dropping, smoothing or just generally messing up the coil pulse signal.

[david beer]

The positive at the otter is through the relays in the fusebox, so will drop as you introduce load, of course this goes to neg when the otter switch shorts. If you want a ign feed, remove the relays and link 85-86.

[GreenV8S]

You could replace the original fan relay with a link wire, that would feed 12v to the otter switch wire, and use that to supply your relays. Of course if you connected that to the original otter switch (or anything else that went to earth) you'd blow something up.

Don't think even in your wildest dreams of taking 12v from the AFM or anything else to do with the engine management system. It's trivially easy to run another 12v from the fuse box if you need it.

[ruaricoles]

Thanks for all the suggestions guys - I'll have a rummage around in the passenger footwell this evening......

Ruari

[ruaricoles]

david beer said:

If you want a ign feed, remove the relays and link 85-86.

Hello David,

I've removed the original fan relay and connected 85-86 - which means the original otter positive feed now works the new fans properly (great) except that now the ignition won't go off! (until I pull out the link wire that is)

I'm definitely confused now....... - any suggestions appreciated!

Ruari

[spend]

I did something like this:
http://foo3.dspen.com/twinfan2.png

If it helps (a picture tells a 1000 words )

Dave

[ruaricoles]

Thanks Dave - I haven't followed that all the way through but I think my relay set up is similar,

I've used 3 big normal relays and a single change-over type to make a circuit like the one here
www.juracid.demon.co.uk/lr/twin_fans.html

and a 2-stage thermostatic switch from these guys
www.x-eng.co.uk/X-Therm.asp?MID=38

It was tricky getting a change-over relay big enough but found Durite make a 70/100A one.

I tested the switch vs. a proper thermocouple in the top hose this evening and it's spot on. Even the dash gauge doesn't seem too far out. All I need now is a proper ignition live to run to the thermostatic switch (that doesn't mean the ignition stays on!)

I've also moved the air filter/intake into the space under the LH headlamp which looks a very worthwhile improvement over what my car had before. Will take some piccies when I've got the car running again.

Many thanks

Ruari

[spend]

ruaricoles said:

Thanks Dave - I haven't followed that all the way through but I think my relay set up is similar,

I've used 3 big normal relays and a single change-over type to make a circuit like the one here
www.juracid.demon.co.uk/lr/twin_fans.html

and a 2-stage thermostatic switch from these guys
www.x-eng.co.uk/X-Therm.asp?MID=38

It was tricky getting a change-over relay big enough but found Durite make a 70/100A one.

I tested the switch vs. a proper thermocouple in the top hose this evening and it's spot on. Even the dash gauge doesn't seem too far out. All I need now is a proper ignition live to run to the thermostatic switch (that doesn't mean the ignition stays on!)

I've also moved the air filter/intake into the space under the LH headlamp which looks a very worthwhile improvement over what my car had before. Will take some piccies when I've got the car running again.

Many thanks

Ruari

There is a bare spade on the back of the fuse box which is ignition (linked to fuse 16 IIRC which may be free depending on your loom). Not all otter switches are powered by the horn circuit, I think some even used the ecu fuse.

70A relays are not used for many things (apart from main ignition the only thing I can think of is Glow plugs!) are you sure this is for cooling fans?

A single twin otter switch is subject to common failure, IMHO existing swirl tank, and bung in rad is better on dual circuits.

I suggest you remove your link, power up the fans by hand and see if you are getting the 12v back down the otter switch connection at the fusebox. I would guess you have done something wrong - draw & re-draw your circuit and you will find it.

Dave

[david beer]

If the ignition is staying on, put a diode in the link wire in the fuse box. Sounds like you have done something wrong with the new set up, all good stuff though.

[spend]

Not wanting to p155 on fires, but in all honesty I think some counterpoints are required for balance...

Its all good fun, but at the end of the day if your cooling system is not working its a waste of time - just more possible points of failure... The only valid points I can see are a bit of shunt when fans kick in (quite re-assuring really) and cooling under the bonnet (ceramic exhaust proliferation goes a long way to nullify this). 2 otter switches and fuses / relays for each fan provides more resiliency and less shunt anyway. Coupled with an override switch it suffices well enough IMHO. I'm sure a large part of the success of Davids kit is the switching on temp from the return hose - which gives far better control IMHO.

Dave

[ruaricoles]

Thanks for all the suggestions again - I'll keep fiddling!

Dave,

The fans I've fitted are 750W Freelander ones, used more because of availability (free) rather than anything else, and they're much quieter as well as being more powerful than the originals. They're also fully sealed, so no more water ingress and corrosion. 750W flat out means 55A or so though, hence the big relays. On the original car they're PWM controlled.

I agree with your comments on the system as a whole though - if it aint broke, then don't fix it - however, mine did break (!) (well, one of the fans corroded and seized) so I thought I'd take the opportunity to make the system even better with much more headroom than standard. I have some responsibility for cooling systems for a vehicle manufacturer so perhaps I'm paranoid about these things!

I'll look for that spade connector, if not I'll try a diode (thanks to Dave B for that suggestion).

Thanks also for the reliability warning re. the 2-stage otter; I've already made a little link lead to carry in the tool kit to bypass the switch if required so hopefully this is a get-out-of-jail card in that respect.

I'm pretty confident I've got my wiring additions right, but previous owners have clearly fiddled with the fuse box area too so perhaps there's a funny from somewhere previously. Certainly my ignition lights sometimes stay on if I turn the ignition on then off again without starting the engine - I had previously assumed this was the alternator as turning the engine slightly on the starter always fixes it - but perhaps this new problem is related to that old one.......

Ta!

Ruari

[ruaricoles]

spend said:

I'm sure a large part of the success of Davids kit is the switching on temp from the return hose - which gives far better control IMHO.

I don't disagree that the system works well (because obviously it does!) but one potential problem with this is that if the fans are working well then the cooling effect based on bottom hose temp will very quickly switch the fans off again as the rad outlet cools before the engine is cold enough.

Ultimately what I want to do is fit a PRT (pressure relief thermostat) which goes into the bottom hose but uses a bypass from top hose to control the opening and also open with pressure, ie. if you rev the engine when the stat is otherwise closed. They're found on Td5 Defenders and a few other cars (MGF I think?), a clever system which helps smooth out cooling performance and pre-empt hot running conditions.

Another job for the list.....

Ruari

[GreenV8S]

ruaricoles said:

spend said:

I'm sure a large part of the success of Davids kit is the switching on temp from the return hose - which gives far better control IMHO.

I don't disagree that the system works well (because obviously it does!) but one potential problem with this is that if the fans are working well then the cooling effect based on bottom hose temp will very quickly switch the fans off again as the rad outlet cools before the engine is cold enough.

Ultimately what I want to do is fit a PRT (pressure relief thermostat) which goes into the bottom hose but uses a bypass from top hose to control the opening and also open with pressure, ie. if you rev the engine when the stat is otherwise closed. They're found on Td5 Defenders and a few other cars (MGF I think?), a clever system which helps smooth out cooling performance and pre-empt hot running conditions.

Another job for the list.....

Ruari

I'm using PEM101020, not a PRT but an earlier version that the PRT was derived from. It works well, but I'd rather use a PRT if I could get one in the right temperature range.

Switching the fans on the rad outlet temperature is exactly the right answer because this temperature tells you whether there is enough cold air flow through the radiator. If there is enough air flow then you don't need the fans on regardless of engine temperature e.g. if you have been sitting in traffic and then move off, the fans can be switched off straight away even if the engine hasn't cooled down yet. Conversely if you come to a stop the rad outlet temperature will shoot up immediately due to zero air flow, this can switch the fans on immediately without waiting for the engine temperature to go out of range.

[spend]

GreenV8S said:

I'm using PEM101020, not a PRT but an earlier version that the PRT was derived from. It works well, but I'd rather use a PRT if I could get one in the right temperature range.

Blinkin Heck Pete!, by the time you get a laminova in - You'll be joining our ranks in that you wont be able to dance a jig round your engine bay

Dave

[GreenV8S]

spend said:

GreenV8S said:

I'm using PEM101020, not a PRT but an earlier version that the PRT was derived from. It works well, but I'd rather use a PRT if I could get one in the right temperature range.

Blinkin Heck Pete!, by the time you get a laminova in - You'll be joining our ranks in that you wont be able to dance a jig round your engine bay

Dave

There's a bit more space now I've got rid of the EWP, but it's still fairly busy in there with all the cr@p from the blower on top/in front of the engine, the extra drive belt, WI, cooling tanks etc.

[spend]

GreenV8S said:

There's a bit more space now I've got rid of the EWP, but it's still fairly busy in there with all the cr@p from the blower on top/in front of the engine, the extra drive belt, WI, cooling tanks etc.

You're getting worse than those old pharoahs & their Pyramids, Peter
Who said 'you cant take it with you'

Dave

[ruaricoles]

GreenV8S said:

I'm using PEM101020, not a PRT but an earlier version that the PRT was derived from. It works well, but I'd rather use a PRT if I could get one in the right temperature range.

Apparently it's the one in the black casing you want (some Rovers I think, and maybe outgoing Freelander Td4), which should control top hose to around 84deg. The creamy coloured alternative is more common (Defender) but I understand the spring in it isn't suitable for the relatively weedy water pump on the RV8 and at around 92deg top hose control it might be a little warm. So says the inventor, anyway!

Ruari

[GreenV8S]

ruaricoles said:

So says the inventor, anyway!

Ruari

You know Bill?